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I just put orders in for a few new iPhone 4S upgrades for the wife and I but I'm not sure how to keep her data (app data mainly, the other essentials are synced with outlook).

She has an iPhone 3G, so can't upgrade to iOS 5 then backup where my 3GS phone can. Can an iTunes backup of her 4.2.1 (latest she can get) iOS be restored to a newer iOS 5 phone, or will it only work on an equivalent 4.2.1 iOS-running device? Or...is there another series of steps to make that possible?

If not, is there a completely different way to get her app data off the phone and onto her new one?

Aside: I realize I can test this as soon as the phones actually arrive...but we're sending the current ones off for resale as soon as possible after getting the long-awaited upgrades. For that, I'm trying to get anything I may need to order for the transfer, etc. taken care of ahead of time.

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  • I don't think that information is known as of yet, but probably given previous updates.
    – ConstantineK
    Commented Oct 8, 2011 at 11:26
  • @hobs - I've never actually been in a mismatch situation (always upgraded then baked up)...so this worked in previous version upgrades of iOS? I had trouble finding anything definitive on that I'm my googling before asking here.
    – Nick Craver
    Commented Oct 8, 2011 at 11:32
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    iTunes and iOS do not support installing iOS 4.3 backups onto devices using earlier versions of iOS. -support.apple.com/kb/ht1766 Basically implies that you can restore earlier versions of the OS on the phone, just not backwards. Also support.apple.com/kb/TS3682 goes more into depth on why 4.3 is an exception to the rule.
    – ConstantineK
    Commented Oct 8, 2011 at 11:38

3 Answers 3

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Yes, this is possible. The backups themselves contain application data and other information that isn't particularly version-specific (with the exception of going from 4.3 backwards, as pointed out by hobs above).

In fact, I had to do this exact process recently, going from 4.2.1 to an iOS 5.0 gold master on an iPhone using a backup, and it went off without a hitch. Developers who want to install a prerelease OS version must put their devices in recovery mode, clean install the OS, then restore application data and settings from a backup. I did this for my iPhone, which I hadn't upgraded to the latest 4.x OS, and everything came across cleanly to iOS 5.0.

The one thing to watch out for is that if you don't encrypt your backups (by selecting the "Encrypt iPhone backup" option in iTunes), your device's keychain will not be transferred to the new device. For non-encrypted backups, the keychain is only preserved when restoring onto the same device you backed up from.

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  • Ah excellent news - testing the exact upgrade we have to do. Good note on the encryption as well, since this definitely won't be to the same device. Thanks!
    – Nick Craver
    Commented Oct 8, 2011 at 15:02
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Yes, you can. You can restore a backup from an earlier version of iOS to the current one. (I had to do it a few times on test devices in the past.)

In those cases, what I had:

  • Devices with iOS x-1 synced and backed up.
  • Devices restored to iOS x
  • Devices synced and data restored from the backups (as iTunes usually lets you do)

You can be very confident that in your case it will work.

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One other possibility would be to make sure her 3G and your 3GS have the same OS version, and then restore her backup to your device. Then upgrade the 3GS to iOS 5, take a backup and restore it unto the 4S.

Doesn't look like this would be necessary in this case, but if all else fails, that might be a way to do it.

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